A local area network (LAN) is a computer network that spans a relatively small area. Most LANs are confined to a single building or group of buildings. LANs can be interconnected by a wide-area network (WAN). Networks can connect nodes such as workstations, personal computers, printers, entertainment nodes, generally ‘nodes’. Networks enable connected nodes to send and receive data.
Carrier sense multiple access/collision detection (CSMA/CD) is technique used to determine how multiple nodes share a single communication channel. A node having data to transmit first checks if the channel is free. If true, the node transmits data. Otherwise, if false, the node waits a random amount of time, and then checks again. If the channel is still busy, then the delay time is increased, and so forth, until the channel becomes free.
A wireless local area network (WLAN) is a shared-medium communication network that transmits information over wireless channels. One standard for a WLAN is IEEE 802.11. IEEE 802.11 networks can be configured arranged in an ad hoc and an infrastructure mode. In ad hoc mode, nodes communicate directly with each other. In infrastructure mode, access points (AP), e.g., base stations, are used to connect nodes to a distribution system (DS), and nodes communicate indirectly via the AP.
The medium access control (MAC) method for 802.11 uses a distributed coordination function (DCF). The DFC is based on carrier sense multiple access/collision avoidance (CSMA/CA) protocol, because collision detection is difficult in wireless transmissions. However, CSMA/CA generates additional overhead and consumes network bandwidth.
To gain access, the MAC Layer checks a network allocation vector (NAV). Each node maintains its own NAV. The vector represents the amount of time waited to send the last packet. The NAV must be zero before a station can attempt to send a next packet. That is, if NAV=0, the channel is not busy, a non-zero value indicates that the channel is busy. Prior to transmitting the packet, the node calculates the amount of time necessary to send the packet based on the packet's length and data rate. The station places a value representing this time in the header of the packet. The receiving node uses the header for setting its own NAVs.
A proposed IEEE 802.11e standard adds a new function called hybrid coordination function (HCF). The HCF uses both a contention-based channel access method, called the enhanced distributed channel access (EDCA) mechanism for contention based transfer and a controlled channel access (HCCA) mechanism for contention free transfer. In EDCA, four channel access categories (ACs) prioritize packet flows.
The differentiated medium access control of EDCA is implemented by assigning different arbitration inter-frame spaces (AIFS) and contention windows (CW) to different ACs. An AC with higher priority is assigned a smaller AIFS and shorter CW to increase the likelihood that higher priority packets are transmitted before lower-priority packets.
In order to protect existing packet flows and optimize network performance, the 802.11e draft standard also describes a distributed admission control method. A node sends an admission request for a particular packet flow to the AP. On receipt of the request, the AP decides whether or not to accept the request. That admission control method performs well in term of protecting packet flows. However, the method is complicated to implement, and cannot be used in ad hoc networks lacking an AP.
A number of channel measurement-based admission control methods are known. Elek et al., in “Admission control based on end-to-end measurements,” Proceeding IEEE INFOCOM, 2000, requires the sender to transmit probe packets to the receiver. The probe packets are to characterize the flow of data packets that are to be sent later. The receiver measures the arrival of the probe packets and constructs a measurement report for the sender. The sender than makes an admission decision based on the report. That method relies on the receiver's measurements.
Bianchi et al., in “Throughput analysis of end-to-end measurement-based admission control in IP,” Proceeding IEEE INFOCOM, 2000, perform admission control by first sending low priority probing packets to a receiver. The receiver measures arrival statistics, e.g., average arrival rate, of the probing packets over a fixed time interval and makes a decision whether or not there are sufficient resources to support data packet. If there are sufficient resources, then the receiver notifies the transmitter that data transmission can start by sending a feedback packet. That method relies on the receiver's decision.
Qiu et al., in “Measurement-based admission control with aggregate traffic envelopes,” IEEE/ACM Trans. Networking, vol. 9, pp. 199-210, April 2001, also measures packet arrival rates in a receiver to determine a traffic envelope, and make admission control decisions. In that method, the sender must first send RSVP packets. The receiver sets packet classifier and scheduling parameters to be used for the data packets.
Jamin et al., in “A Measurement-based Admission Control Algorithm for Integrated Services Packet Networks (Extended Version),” ACM/IEEE Transactions on Networking, December 1996, measure packet delays and packet rates, using a token bucket technique, to make admission decisions.
U.S. Patent Application 20030031129 by Dutkiewicz et al., on Feb. 13, 2003 “Network packet flow admission control,” operates by having the sender transmit a packet flow request. The request includes a transmission rate and a required performance level. The receiver determines a maximum allowable transmission rate associated with a maximum performance level, and a number of active nodes including currently active and requesting node, these values are compared with an admission boundary and an admission decision is made accordingly.
There are a number of problems with prior art admission control methods. Some methods require centralized management for making admission decision. Such methods can operate only in infrastructure mode networks. Those methods are of no use to ad hoc networks where there is no centralized management. Other methods are active methods, in that they require the sender to transmit probe or request packets through the network before admission is allowed. That has two problems, first the amount of network traffic is increased, and second the probing induces delays before data can actually be transmitted. Furthermore, in some of those methods, the measuring based on the probe traffic is done in the receiver. And in some cases, it is the receiver that makes the decision whether to admit or not.
Therefore, there is a need for a passive admission control method that is entirely under control of the sender, and that does not increase network traffic to effect admission. Furthermore, it is desired to distribute the admission control over the network in cases where the network lacks an infrastructure.